As a construction machine equipped with an exhaust gas purifying system, there has been known a type which comprises a muffler provided with a reducing catalyst, and a liquid reductant tank for storing a liquid reductant, such as an aqueous urea solution, to be supplied to an upstream side of the reducing catalyst to accelerate a reduction reaction. In this type of construction machine, the liquid reductant, which is consumed at a rate proportional to consumption of fuel (e.g., several % of fuel) is generally replenished at the same timing as that of replenishment of fuel. Hence, for improvement of fuel and liquid reductant replenishment efficiency, it is desirable to install the liquid reductant tank closely to a fuel tank. Moreover, since quality and performance of the liquid reductant vary with temperature, it is desirable that the liquid reductant tank is installed in an environment almost free of influence of external heat, such as solar heat, engine heat and heat of ambient air, i.e., in a shielded environment.
Heretofore, for allowing the liquid reductant to be installed in the environment satisfying the above condition in a construction machine such as a hydraulic shovel, known is a technique of providing an openable and closable tool storage box close to a fuel tank disposed on an upper frame of an upper slewing body in the construction machine and arranging a liquid reductant tank within the tool storage box.
This conventional technique, however, has the following disadvantages A and B.
(A) A replenishment port of the liquid reductant tank is positioned at a position fairly lower than a filler port of the fuel tank, which complicates an operation of replenishing the liquid reductant from a replenishment tank, such as a plastic tank, to the liquid reductant tank. Specifically, the liquid reductant tank, required to have only a small capacity, has a significantly small size and a small height, as compared to the fuel tank. On the other hand, according to the above conventional technique, where the liquid reductant tank is installed within the toll storage box installed on the same plane as that of the fuel tank, the replenishment port of the liquid reductant tank inevitably becomes fairly lower than the filler port of the fuel tank. Using, as measures therefor, a special tank table to raise a height position of the replenishment port of the liquid reductant tank leads to significant increases in cost and required space.
(B) The technique involves a significant reduction in capacity of the fuel tank. The conventional technique requires enlarging a planar size of the tool storage box in order to house the liquid reductant tank therein, which inevitably leads to a reduction in planar size of the fuel tank to be disposed in side-by-side relation to the tool storage box within a limited space. Thus, the capacity of the fuel tank is significantly reduced, thereby shortening a time period in which a continuous construction work can be performed.